ABSTRACT
This chapter discusses how the control terms themselves react with each other, and the effect that these control-term interactions have on the process itself. It provides the characteristics of some commonly used instruments and control devices, and aims to develop the combination of these interactions in a realistic application to a process. The effectiveness, or the results obtained at a practical level when an interactive controller is in operation of the three-term adjustments, illustrates the interaction. The frequency response method was in fashion in the 1950s. The analysis comprised disconnecting the pneumatic signal from the controller to the control device and replacing it with a fixed pressure of a magnitude that maintained the process at the desired value. The control signal to the correcting device is disconnected from the controller but is then instead connected to a manual loading station.
